THEORETICAL ASPECTS OF MPD THRUSTER SCALING.

A one-dimensional MPD channel flow model developed to predict the performance of MPD thruster prototypes is presented. The model accounts for real gas effects and was applied to argon gas and ablated Teflon. The model was extended to allow the analysis of coaxial electrode configurations. Nondimensional solutions are shown to depend on the magnetic Reynolds number and other nondimensional parameters related to propellant characteristics and inlet conditions. Similitude and scaling criteria derived from the analysis are presented. Onset phenomena are discussed in the light of the model's outcomes. Both anode sheath failure caused by axial current conduction and current concentration at the cathode tip and base caused by excessive back EMF participate in erosion processes but the latter effect is deemed predominant in determining the onset limit. On this assumption, a quantitative relationship is derived between critical current density and thruster geometry and operating conditions.